Radial Evolution of a CIR: Observations From a Nearly Radially Aligned Event Between Parker Solar Probe and STEREO‐A

AbstractDirect numerical simulation (DNS) of an impinging jet flow with a nozzle-to-plate distance of two jet diameters and a Reynolds number of 10 000 is carried out at high spatial resolution using high-order numerical methods. The flow configuration is designed to enable the development of a fully turbulent regime with the appearance of a well-marked secondary maximum in the radial distribution of the mean heat transfer. The velocity and temperature statistics are validated with documented experiments. The DNS database is then analysed focusing on the role of unsteady processes to explain the spatial distribution of the heat transfer coefficient at the wall. A phenomenological scenario is proposed on the basis of instantaneous flow visualisations in order to explain the non-monotonic radial evolution of the Nusselt number in the stagnation region. This scenario is then assessed by analysing the wall temperature and the wall shear stress distributions and also through the use of conditional averaging of velocity and temperature fields. On one hand, the heat transfer is primarily driven by the large-scale toroidal primary and secondary vortices emitted periodically. On the other hand, these vortices are subjected to azimuthal distortions associated with the production of radially elongated structures at small scale. These distortions are responsible for the appearance of very high heat transfer zones organised as cold fluid spots on the heated wall. These cold spots are shaped by the radial structures through a filament propagation of the heat transfer. The analysis of probability density functions shows that these strong events are highly intermittent in time and space while contributing essentially to the secondary peak observed in the radial evolution of the Nusselt number.

Download Full-text

On the Radial Evolution of Alfvénic Turbulence in the Solar Wind

Space Science Reviews ◽

10.1007/s11214-006-5232-8 ◽

2006 ◽

Vol 122 (1-4) ◽

pp. 321-328 ◽

Cited By ~ 12

Author(s):

Roberto Bruno ◽

Bruno Bavassano ◽

Raffaella D’amicis ◽

Vincenzo Carbone ◽

Luca Sorriso-Valvo ◽

...

Keyword(s):

Solar Wind ◽

Radial Evolution

Download Full-text

The formation and evolution of the electron strahl in the inner heliosphere

10.5194/egusphere-egu21-5152 ◽

2021 ◽

Author(s):

Seong-Yeop Jeong ◽

Daniel Verscharen ◽

Vocks Christian ◽

Christopher Owen ◽

Robert Wicks ◽

...

Keyword(s):

Solar Wind ◽

Velocity Distribution Function ◽

Electron Velocity ◽

Electron Velocity Distribution ◽

Electron Velocity Distribution Function ◽

Coulomb Collisions ◽

Spiral Geometry ◽

Formation And Evolution ◽

Radial Evolution ◽

Inner Heliosphere

The electrons in the solar wind exhibit an interesting kinetic substructure with many important implications for the overall energetics of the plasma in the heliosphere. We are especially interested in the formation and evolution of the electron strahl, a field-aligned beam of superthermal electrons, in the heliosphere. We develop a kinetic transport equation for typical heliospheric conditions based on a Parker-spiral geometry of the magnetic field. We present the results of our theoretical model for the radial evolution of the electron velocity distribution function (VDF) in the solar wind. We study the effects of the adiabatic focusing of energetic electrons, wave-particle interactions, and Coulomb collisions through a generalized kinetic equation for the electron VDF. We compare and contrast our results with the observed effects in the electron VDFs from space missions that explore the radial evolution of electrons in the inner heliosphere such as Helios, Parker Solar Probe, and Solar Orbiter.

Download Full-text

Evolution of the MHD turbulence properties in the inner heliosphere with the PSP/SolO alignment data

10.5194/egusphere-egu21-14585 ◽

2021 ◽

Author(s):

Daniele Telloni ◽

Keyword(s):

Solar Wind ◽

High Frequency ◽

Interplanetary Space ◽

Solar Wind Plasma ◽

Radial Dependence ◽

Physical Processes ◽

Temperature Anisotropy ◽

Mhd Turbulence ◽

Radial Evolution ◽

Inner Heliosphere

Radial alignments between pairs of spacecraft is the only way to observationally investigate the turbulent evolution of the solar wind as it expands throughout interplanetary space. On September 2020 Parker Solar Probe (PSP) and Solar Orbiter (SolO) were nearly perfectly radially aligned, with PSP orbiting around its perihelion at 0.1 au (and crossing the nominal Alfv&#233;n point) and SolO at 1 au. PSP/SolO joint observations of the same solar wind plasma allow the extraordinary and unprecedented opportunity to study how the turbulence properties of the solar wind evolve in the inner heliosphere over the wide distance of 0.9 au. The radial evolution of (i) the MHD properties (such as radial dependence of low- and high-frequency breaks, compressibility, Alfv&#233;nic content of the fluctuations), (ii) the polarization status, (iii) the presence of wave modes at kinetic scale as well as their distribution in the plasma instability-temperature anisotropy plane are just few instances of what can be addressed. Of furthest interest is the study of whether and how the cascade transfer and dissipation rates evolve with the solar distance, since this has great impact on the fundamental plasma physical processes related to the heating of the solar wind. In this talk I will present some of the results obtained by exploiting the PSP/SolO alignment data.

Download Full-text

Theory and observations of switchbacks’ evolution in the solar wind

10.5194/egusphere-egu21-13400 ◽

2021 ◽

Author(s):

Anna Tenerani ◽

Marco Velli ◽

Lorenzo Matteini

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Radial Magnetic Field ◽

Open Questions ◽

Coronal Activity ◽

Turbulent Heating ◽

Field Lines ◽

Radial Evolution ◽

Field Correlation

Alfv&#233;nic fluctuations represent the dominant contributions to turbulent fluctuations in the solar wind, especially, but not limited to, the fastest streams with velocity of the order of 600-700 km/s. Alfv&#233;nic fluctuations can contribute to solar wind heating and acceleration via wave pressure and turbulent heating. Observations show that such fluctuations are characterized by a nearly constant magnetic field amplitude, a condition which remains largely to be understood and that may be an indication of how fluctuations evolve and relax in the expanding solar wind. Interestingly, measurements from Parker Solar Probe have shown the ubiquitous and persistent presence of the so-called switchbacks. These are magnetic field lines which are strongly perturbed to the point that they produce local inversions of the radial magnetic field. The corresponding signature of switchbacks in the velocity field is that of local enhancements in the radial speed (or jets) that display the typical velocity-magnetic field correlation that characterizes Alfv&#233;n waves propagating away from the Sun.&#160;While there is not yet a general consensus on what is the origin of switchbacks and their connection to coronal activity, a first necessary step to answer these important questions is to understand how they evolve and how long they can persist in the solar wind. Here we investigate the evolution of switchbacks. We address how their evolution is affected by parametric instabilities and the possible role of expansion, by comparing models with the observed radial evolution of the fluctuations&#8217; amplitude. We finally discuss what are the implications of our results for models of switchback generation and related open questions.

Download Full-text

Radial Evolution of Interaction Regions

Physics of the Outer Heliosphere - COSPAR Colloquia Series ◽

10.1016/b978-0-08-040780-7.50045-2 ◽

1990 ◽

pp. 245-248 ◽

Cited By ~ 1

Author(s):

Y.C. Whang ◽

L.F. Burlaga

Keyword(s):

Interaction Regions ◽

Radial Evolution

Download Full-text

The evolution of inverted magnetic fields through the inner heliosphere

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa951 ◽

2020 ◽

Vol 494 (3) ◽

pp. 3642-3655 ◽

Cited By ~ 2

Author(s):

Allan R Macneil ◽

Mathew J Owens ◽

Robert T Wicks ◽

Mike Lockwood ◽

Sarah N Bentley ◽

...

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Radial Distance ◽

Occurrence Rate ◽

Slow Solar Wind ◽

The Sun ◽

Radial Evolution ◽

In Transit ◽

The Magnetic Field ◽

Inner Heliosphere

ABSTRACT Local inversions are often observed in the heliospheric magnetic field (HMF), but their origins and evolution are not yet fully understood. Parker Solar Probe has recently observed rapid, Alfvénic, HMF inversions in the inner heliosphere, known as ‘switchbacks’, which have been interpreted as the possible remnants of coronal jets. It has also been suggested that inverted HMF may be produced by near-Sun interchange reconnection; a key process in mechanisms proposed for slow solar wind release. These cases suggest that the source of inverted HMF is near the Sun, and it follows that these inversions would gradually decay and straighten as they propagate out through the heliosphere. Alternatively, HMF inversions could form during solar wind transit, through phenomena such velocity shears, draping over ejecta, or waves and turbulence. Such processes are expected to lead to a qualitatively radial evolution of inverted HMF structures. Using Helios measurements spanning 0.3–1 au, we examine the occurrence rate of inverted HMF, as well as other magnetic field morphologies, as a function of radial distance r, and find that it continually increases. This trend may be explained by inverted HMF observed between 0.3 and 1 au being primarily driven by one or more of the above in-transit processes, rather than created at the Sun. We make suggestions as to the relative importance of these different processes based on the evolution of the magnetic field properties associated with inverted HMF. We also explore alternative explanations outside of our suggested driving processes which may lead to the observed trend.

Download Full-text